Recently, there are significant interests in improving scratch damages of polymeric and coating materials because they are more susceptible to scratch damages on the surface than metals. In general, scratches are regarded as visible surface damages and grooves that the human eyes can perceive. It is well known that a number of factors such as scratch mode, scratch velocity, surface hardness, surface roughness, temperature, scratch tip geometry, fillers and additives have effects on the scratch behaviors. Especially, although mar and scratch-induced damages on the material surface are visually perceivable, it is rather troublesome to accurately and quantitatively evaluate the surface damage. Accordingly, there has been a growing concern on methods enabling precise and quantitative evaluation of scratch property of polymeric and coating materials.
The current evaluation standards including ASTM (D7027-05) and ISO (19252:2008) introduce quantitative evaluation of scratch-induced surface damage of materials. But, these standard methods emphasize only the methodological aspects of scratch formation based on experiments and focused on observation of the shape of the surface damage.
For example, ISO 19252 evaluates scratch-induced surface damage, based on the apparent shape of the trace of a scratch tip, such as ploughing, wedge formation, and cutting.
However, since such a surface damage evaluation method is subjective and dependent on the competency of the observer, the obtained results may be not reproducible, meaningful while not ensuring objectivity.
Mars occur when a relatively low load is applied to a material surface. If the load is increased beyond a certain limit, whitening phenomenon occurs. According to ASTM D7027-05, the normal load at this time point, referred to as a critical normal load, is measured to quantitatively evaluate the surface damage.
However, since the critical normal load is not a normalized value. They are scratch tip geometry dependent. In other words, a new value (i.e., material property) that normalized by the corresponding contact area, similar to the definition of yield stress (N/m2) and impact resistance (J/m), needs to be expressed to quantify the whitening point and the initiation of cutting. Therefore, there are some problems on the reproducibility, objectivity, reliability and discrimination of results. In this context, the critical normal load is not appropriate as a factor of the quantification.
Accordingly, a more effective and quantitative evaluation method for evaluating scratch-induced surface damage of a material or its visibility is required.